From: Christopher Dykes <cdykes@fb.com>
Date: Thu, 16 Feb 2017 21:08:47 +0000 (-0800)
Subject: Use std::this_thread::yield rather than sched_yield
X-Git-Tag: v2017.03.06.00~32
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=folly.git;a=commitdiff_plain;h=79b78eaaf88ead9fa6543822c193b4e86d0e2395

Use std::this_thread::yield rather than sched_yield

Summary: They do the same thing, and the first is portable.

Reviewed By: yfeldblum

Differential Revision: D4569649

fbshipit-source-id: db0434766f674a7789d6e59335e122b4d2131e06
---

diff --git a/folly/RWSpinLock.h b/folly/RWSpinLock.h
index c4905d1d..63dac2f5 100644
--- a/folly/RWSpinLock.h
+++ b/folly/RWSpinLock.h
@@ -156,11 +156,11 @@ pthread_rwlock_t Read        728698     24us       101ns     7.28ms     194us
 #undef RW_SPINLOCK_USE_SSE_INSTRUCTIONS_
 #endif
 
+#include <algorithm>
 #include <atomic>
 #include <string>
-#include <algorithm>
+#include <thread>
 
-#include <sched.h>
 #include <glog/logging.h>
 
 #include <folly/Likely.h>
@@ -194,7 +194,7 @@ class RWSpinLock {
   void lock() {
     int count = 0;
     while (!LIKELY(try_lock())) {
-      if (++count > 1000) sched_yield();
+      if (++count > 1000) std::this_thread::yield();
     }
   }
 
@@ -208,7 +208,7 @@ class RWSpinLock {
   void lock_shared() {
     int count = 0;
     while (!LIKELY(try_lock_shared())) {
-      if (++count > 1000) sched_yield();
+      if (++count > 1000) std::this_thread::yield();
     }
   }
 
@@ -226,7 +226,7 @@ class RWSpinLock {
   void lock_upgrade() {
     int count = 0;
     while (!try_lock_upgrade()) {
-      if (++count > 1000) sched_yield();
+      if (++count > 1000) std::this_thread::yield();
     }
   }
 
@@ -238,7 +238,7 @@ class RWSpinLock {
   void unlock_upgrade_and_lock() {
     int64_t count = 0;
     while (!try_unlock_upgrade_and_lock()) {
-      if (++count > 1000) sched_yield();
+      if (++count > 1000) std::this_thread::yield();
     }
   }
 
@@ -601,7 +601,7 @@ class RWTicketSpinLockT {
    * turns.
    */
   void writeLockAggressive() {
-    // sched_yield() is needed here to avoid a pathology if the number
+    // std::this_thread::yield() is needed here to avoid a pathology if the number
     // of threads attempting concurrent writes is >= the number of real
     // cores allocated to this process. This is less likely than the
     // corresponding situation in lock_shared(), but we still want to
@@ -610,7 +610,7 @@ class RWTicketSpinLockT {
     QuarterInt val = __sync_fetch_and_add(&ticket.users, 1);
     while (val != load_acquire(&ticket.write)) {
       asm_volatile_pause();
-      if (UNLIKELY(++count > 1000)) sched_yield();
+      if (UNLIKELY(++count > 1000)) std::this_thread::yield();
     }
   }
 
@@ -623,7 +623,7 @@ class RWTicketSpinLockT {
     // there are a lot of competing readers.  The aggressive spinning
     // can help to avoid starving writers.
     //
-    // We don't worry about sched_yield() here because the caller
+    // We don't worry about std::this_thread::yield() here because the caller
     // has already explicitly abandoned fairness.
     while (!try_lock()) {}
   }
@@ -653,13 +653,13 @@ class RWTicketSpinLockT {
   }
 
   void lock_shared() {
-    // sched_yield() is important here because we can't grab the
+    // std::this_thread::yield() is important here because we can't grab the
     // shared lock if there is a pending writeLockAggressive, so we
     // need to let threads that already have a shared lock complete
     int count = 0;
     while (!LIKELY(try_lock_shared())) {
       asm_volatile_pause();
-      if (UNLIKELY((++count & 1023) == 0)) sched_yield();
+      if (UNLIKELY((++count & 1023) == 0)) std::this_thread::yield();
     }
   }
 
diff --git a/folly/configure.ac b/folly/configure.ac
index a38ea92c..f08d6c2f 100644
--- a/folly/configure.ac
+++ b/folly/configure.ac
@@ -564,7 +564,6 @@ AC_CHECK_FUNCS([getdelim \
                 memset \
                 pow \
                 strerror \
-                sched_yield \
                 malloc_size \
                 malloc_usable_size \
                 memrchr \
diff --git a/folly/io/async/EventBase.cpp b/folly/io/async/EventBase.cpp
index a493d928..941cdeec 100644
--- a/folly/io/async/EventBase.cpp
+++ b/folly/io/async/EventBase.cpp
@@ -27,6 +27,7 @@
 #include <condition_variable>
 #include <fcntl.h>
 #include <mutex>
+#include <thread>
 
 namespace folly {
 
@@ -231,7 +232,7 @@ getTimeDelta(std::chrono::steady_clock::time_point* prev) {
 
 void EventBase::waitUntilRunning() {
   while (!isRunning()) {
-    sched_yield();
+    std::this_thread::yield();
   }
 }
 
diff --git a/folly/test/CacheLocalityBenchmark.cpp b/folly/test/CacheLocalityBenchmark.cpp
index 9522be68..dbb2d6ac 100644
--- a/folly/test/CacheLocalityBenchmark.cpp
+++ b/folly/test/CacheLocalityBenchmark.cpp
@@ -16,11 +16,12 @@
 
 #include <folly/detail/CacheLocality.h>
 
-#include <sched.h>
 #include <memory>
 #include <thread>
 #include <unordered_map>
+
 #include <glog/logging.h>
+
 #include <folly/Benchmark.h>
 
 using namespace folly::detail;
@@ -167,7 +168,7 @@ static void contentionAtWidth(size_t iters, size_t stripes, size_t work) {
 
       ready++;
       while (!go.load()) {
-        sched_yield();
+        std::this_thread::yield();
       }
       std::atomic<int> localWork(0);
       for (size_t i = iters; i > 0; --i) {
@@ -187,7 +188,7 @@ static void contentionAtWidth(size_t iters, size_t stripes, size_t work) {
   }
 
   while (ready < numThreads) {
-    sched_yield();
+    std::this_thread::yield();
   }
   braces.dismiss();
   go = true;
@@ -208,7 +209,7 @@ static void atomicIncrBaseline(size_t iters,
   while (threads.size() < numThreads) {
     threads.push_back(std::thread([&]() {
       while (!go.load()) {
-        sched_yield();
+        std::this_thread::yield();
       }
       std::atomic<size_t> localCounter(0);
       std::atomic<int> localWork(0);
diff --git a/folly/test/SynchronizedTestLib-inl.h b/folly/test/SynchronizedTestLib-inl.h
index 4b1409d6..99706950 100644
--- a/folly/test/SynchronizedTestLib-inl.h
+++ b/folly/test/SynchronizedTestLib-inl.h
@@ -498,7 +498,7 @@ template <class Mutex> void testConcurrency() {
     // Test lock()
     for (size_t n = 0; n < itersPerThread; ++n) {
       v.contextualLock()->push_back((itersPerThread * threadIdx) + n);
-      sched_yield();
+      std::this_thread::yield();
     }
   };
   runParallel(numThreads, pushNumbers);